1. Field of the Invention
The present invention relates to a sealed package for extending the shelf life of electrodes sealed within the package. Also, the present invention relates to a method for extending the shelf life of electrodes sealed within a package. Furthermore, the present invention relates to a release liner for covering an electrode pad.
2. Description of the Prior Art
Since packaged articles may remain in their packages for extended periods of time, it is often desired to control the conditions within a package. For example, humidity and temperature affect the condition of many packaged articles. Along these lines, packaged articles may require low humidity to help prevent damage or affect functioning. Inclusion of packets of silica gel, which absorb moisture, in many packages evidence the desire to control humidity in packages. The silica gel in a package can help to preserve the articles in a package in a desired state. Along these lines, silica gel absorbs moisture to maintain a dry environment. In other cases, it may be desired to maintain a moister environment in a package.
Sometimes, articles may be required to remain within a certain range in order to maintain a desired state or functionality. One example of such an article is electrode pads for medical uses. For example, electrode pads may include a hydrogel that facilitates their operation. The shelf life of electrode pads is determined in part by the length of time it takes for enough water moisture to evaporate out of the hydrogel and escape the pads package. As moisture escapes, the electrical properties of the electrode pads become increasingly compromised.
In one context, where electrode pads are utilized with a defibrillator, a very significant factor includes changes in small and large signal impedance values between a patient and a defibrillator. As the hydrogel dries out, the impedance values increase, making it more difficult to monitor a patient's electrical signals, obtain transthoracic impedance, and deliver energy into the body.
Water loss can affect the mechanical properties of the hydrogel as well. In some hydrogels, the loss of water causes the hydrogel to skin over or solidify, especially around the edges, which inhibits the ability of the hydrogel to adhere to the skin. This partial or complete loss of adhesion can render an electrode useless since it cannot then create or maintain an effective contact with the patient's skin. Thus, water loss from the electrode pad can prevent or attenuate receipt of electrocardiogram (ECG) signals by a defibrillator. In addition, water loss from the electrode pad can alter the delivery of defibrillation energy from a defibrillator to the patient.
Additionally, poor or uneven contact of the electrode pad with a patient's skin may unduly concentrate energy transfer during defibrillation into areas that exhibit good skin contact. Higher than usual current densities that result from poor or uneven skin contact can cause skin burns. If the current is not delivered to a patient in the manner that an electrode pad was designed for, the resulting treatment delivered to the patient may be altered, compromising patient outcome.
To help ensure that electrode pads will be usable when opened, electrode manufacturers currently print an expiration date on each set of pads. The electrode pads are to be discarded no later than the expiration date. However, the expiration date typically is determined based upon studies of the hydrogel used on the pads, and the amount of water moisture that escapes the package over time under normal as well as strenuous conditions. A safety factor is added to give time for the electrode pads to be shipped from the supplier to an original equipment manufacturer (OEM), and then from the OEM to the customer. This helps to ensure that the electrode pads are always usable, barring any package damage, when removed from the package before the expiration date.
Calculating the expiration date of electrode pads or other components as described above is a conservative method of ensuring quality. However, as a result, the expiration date may arrive before the pads have actually expired. In fact, electrode pads may be usable for much longer than the expiration date, especially if they are kept at room temperature or in a high humidity environment.
The above example only represents one particular example of an electrode pad of a particular use. Electrode pads for other uses may be similarly affected. Also, devices other than electrode pads may be affected by age and package conditions. Furthermore, factors other than humidity, such as corrosion or contaminants, can affect the functionality or shelf life of a device.